Method and apparatus for ash cooling

ABSTRACT

Systems and methods for step-wise cooling high pressure and high temperature ash discharged from the gasifier used for gasification of carboneous materials, wherein a high pressure cooler cools the ash under the operating pressure of the gasifier, which may be followed by a depressurizer which brings the cooled ash to safe-handling temperature. A low temperature ash cooler may also be optionally used. Also provided is a system where a wet scrubber is used to clean the syngas from the gasifier, the waste water blow down from the scrubber is used to cool the hot ash either in the high temperature ash cooler, or the low temperature ash cooler. Steam generated in the ash coolers is supplied back to the gasifier to reduce steam consumption.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/786,614, filed Mar. 15, 2013, which is incorporated by referenceherein in its entirety.

FIELD OF THE INVENTION

The present invention relates to coal gasification using fluidized bedreactor. More specifically, the present invention relates to a methodand apparatus for cooling and handling high temperature and highpressure ash discharged from a fluidized bed gasification reactor. Thepresent invention also relates to a method and apparatus for using wastewater from a syngas scrubber in the cooling of hot ash discharged fromthe gasifier.

BACKGROUND OF THE INVENTION

Gasification of carbon containing or carbonaceous materials is used toproduce syngas, a mixture of carbon monoxide, hydrogen, carbon dioxide,and other components. Various types of gasifiers are known and used,including a moving bed gasifier, entrained flow gasifier, and fluidizedbed gasifier.

Carbonaceous feed materials often contains an appreciable ash content,e.g. above 5 wt %. Non-slagging gasifiers used to convert these feedmaterials commonly operate at temperatures just below the melting pointof the ash, and the ash discharged from the gasifier is at a temperatureranging from 500° C. to 1200° C., and under a high pressure (up to 6bar). This ash must be cooled to ambient temperature, or at least notmore than 300° C. for storage and subsequent handling and disposal.

It has been technically challenging to cool such hot ash under highpressure, because existing equipment capable of handling hot solidsunder high pressure is expensive, difficult to build and operate,unreliable, and requires frequent maintenance. For example, conventionalvalves are not reliable in high temperature, high pressure flowingsolids service.

Furthermore, thermal energy of the hot ash is not efficiently used ornot used at all, imposing a net energy penalty on the system. Often, theash is discharged directly into water at low or ambient pressuresgenerating steam that is either not recovered or has very limitedutility and value due to its low pressure and contamination; or thethermal energy of the hot ash is somehow transferred into cooling water,or using relatively expensive heat transfer equipment to generate lowtemperature/low pressure steam which is also of low value.

There is thus a further need for improved hot ash cooling methods andequipment.

U.S. patent application Ser. No. 13/532,769 provides an apparatus and amethod for capturing and recycling small fines for fluidized bedreactors or gasifiers operated at high temperatures and pressures in areliable and simple manner. However, even after such deliberate steps ofsolids removal, the raw syngas still contains a significant amount ofsolids and must undergo further cleaning processes, for the removal ofresidual solids and undesired gas phase contaminants, such as sulfurcompounds, before it can be used in power generation or the productionof chemicals. A wet scrubber or water scrubber is commonly used for thispurpose, generating a wastewater stream containing salts, dissolvedgases and vapors, and suspended solids. In SES process described in U.S.patent application Ser. No. 13/532,769 (“the SES process”), solids arefirst removed and recycled to the gasifier using cyclones, then a filteris used to remove further solids, and a wet scrubber is lastly used toremove some gas phase contaminants such as halides and any solids thathave passed through the filter due to their small particle size orfailure of filter elements. To prevent buildup of salts and acids orbases in the scrubber water and to limit the concentration of solids inthe scrubber, the scrubbing liquid, typically water, is continuallyadded to and removed from the scrubber, and is henceforth called“makeup” and “blowdown.”

Currently, the wastewater stream resulting from the scrubber blowdown istreated and then discharged. The treatment of wastewater is costly, andthe discharged wastewater represents a substantial portion of theoverall water consumption of the gasification process. There istherefore a need to more fully utilize the carbon content in thewastewater stream from the scrubber, and to reduce the waterconsumption.

SUMMARY OF THE INVENTION

As discussed above, handling high temperature, high pressure flowingsolids is not only costly but also not reliable. Some attempts have beenmade to make improvement, but the results have not been satisfactory.Additionally, these improved cooling solutions also result in waste ofthermal energy and water recourse. The a method and apparatus in thepresent invention can solve the technical problems as mentioned aboveand also raise the overall efficiency of the gasification process.

According one aspect of the present invention, this present inventionprovides a gasification system comprising a fluidized bed gasifier intowhich a carbonaceous feed material is fed, and out of which a productgas stream and a flowable ash is discharged, wherein the gasifier isoperated at a temperature just under a melting point of the ash, andunder a pressure not less than 6 bar gauge, and a high temperature ashcooler which is connected to the gasifier and into which the hot ashunder pressure is discharged, wherein the high temperature ash coolercomprises a water-supplying apparatus that provides water for coolingthe flowable ash, wherein the flowable ash is cooled to a temperaturesuitable for the ash to be handled with conventional carbon steelequipment.

In some embodiment of the gasification system, the water supplyingapparatus supplies the cooling water to the high temperature ash coolerto be in direct contact with the flowable ash, and wherein the systemfurther comprises a controller to control the water supplying apparatusso that the water is vaporized upon direct contact with the ash togenerate steam, and the flowability of the ash is maintained, and theflowable ash is cooled to a temperature not lower than thepre-determined threshold temperature.

In some embodiment of the gasification system, the cooling water issupplied to the high temperature ash cooler and cools the ash viaindirect heat transfer.

In some embodiment of the gasification system, the high temperature ashcooler comprises a cooling jacket, or cooling coils, or a cooling panelthrough which the cooling water flows and absorbs heat indirectly fromthe hot ash.

In some embodiment of the gasification system, a portion of the coolingwater is supplied to the high temperature ash cooler in direct contactwith the flowable ash, and wherein the system further comprises acontroller to control the water supplying apparatus so that the water isvaporized upon direct contact with the ash to generate steam, and theflowability of the ash is maintained; and a portion of the cooling wateris supplied to the high temperature ash cooler where the cooling watercools the ash via indirect heat transfer; and wherein the flowable ashis cooled to a temperature not lower than the pre-determined thresholdtemperature.

In some embodiment of the gasification system, the system furthercomprises a connection between the high temperature ash cooler and thegasifier, wherein steam generated from the water supplied to the hightemperature ash cooler and is supplied to the gasifier.

In some embodiment of the gasification system, the system furthercomprises a depressurizing device which is connected to the hightemperature ash cooler to receive the cooled high pressure ash from thehigh temperature ash cooler, and which is able to reduce the pressure ofthe ash to ambient pressure.

In some embodiment of the gasification system, the depressurizing devicecomprises a double sealed lock hopper.

In some embodiment of the gasification system, the system furthercomprises a second ash cooler device which is connected to the hightemperature ash cooler to receive the cooled high pressure ash from thehigh temperature ash cooler, and which is able to further lower thetemperature of the ash to ambient temperature.

In some embodiment of the gasification system, the system furthercomprises a second ash cooler device which is connected to thedepressurizing device to receive the ash from the high temperature ashcooler, and which is able to further lower the temperature of the ash toambient temperature.

In some embodiment of the gasification system, the system furthercomprises a depressurizing device which is connected to the second ashcooling device to receive the ash from the second ash cooling device,and which is able to reduce the pressure of the ash to ambient pressure.

In some embodiment of the gasification system, the high temperature ashcooler comprises a fluidized bed or a moving bed wherein the highpressure ash makes direct contact with the water from the watersupplying apparatus.

In some embodiment of the gasification system, the water supplyapparatus comprises means to disperse the liquid into the ash such asspray nozzles, atomizing spray nozzles, microporous pipes.

According to another aspect of the present invention, this inventionfurther provides a gasification system comprising a fluidized bedgasifier into which a carbonaceous feed material is fed, and out ofwhich a product gas stream and a flowable ash are discharged, whereinthe gasifier is operated at a temperature just under a melting point ofthe ash, and under a pressure not less than 6 bar gauge, and wherein theproduct gas stream comprises gaseous and particulate pollutants, a wetscrubber for removing the pollutants from the product gas stream andproducing a waste water stream, an ash cooler connected with thegasifier to receive hot ash from the gasifier; and a connection todeliver at least a portion of the waste water stream to the ash cooler,wherein the waste water stream is converted into steam.

In some embodiment of the gasification system, the ash cooler comprisesa high temperature ash cooler connected directly with the gasifier.

In some embodiment of the gasification system, the ash cooler furthercomprises a low temperature ash cooler, and wherein the waste water isdelivered to the low temperature ash cooler.

In some embodiment of the gasification system, the waste water makesdirect contact with the ash and steam generated from the contact isdelivered to the gasifier.

According to another aspect of this present invention, some embodimentprovide a method for cooling ash discharged from a fluidized bedgasifier, wherein a fluidized bed gasifier is fed with a carbonaceousfeed material, and a product gas stream and a flowable ash is dischargedout of the gasifier, wherein the gasifier is operated at a temperaturejust under a melting point of the ash, and under a pressure not lessthan 6 bar gauge, the method comprising cooling the flowable ash to atemperature suitable for the ash to be handled with conventional carbonsteel equipment in a high temperature ash cooler which is connected tothe gasifier and into which the hot ash under pressure is discharged,wherein the high temperature ash cooler comprises a water-supplyingapparatus that provides water for cooling the flowable ash.

In some embodiment of the method, wherein the water supplying apparatussupplies the cooling water to the high temperature ash cooler to be indirect contact with the flowable ash, and the method further comprisescontrolling the water supplying apparatus so that the water is vaporizedupon direct contact with the ash to generate steam, and the flowabilityof the ash is maintained, and the flowable ash is cooled to atemperature not lower than the pre-determined threshold temperature.

In some embodiment of the method, the method further comprises receivingthe cooled high pressure ash from the high temperature ash cooler, andreducing the pressure of the ash to ambient pressure with adepressurizing device which is connected to the high temperature ashcooler.

In some embodiment of the method, the method further comprises receivingthe cooled ambient pressure ash from the a depressurizing device, andfurther lowering the temperature of the ash to ambient temperature witha second ash cooler device which is connected to the depressurizingdevice.

Further, certain embodiments provide a method for cooling ash dischargedfrom a fluidized bed gasifier, wherein a fluidized bed gasifier is fedwith a carbonaceous feed material, and a product gas stream and aflowable ash are discharged out of the gasifier, wherein the gasifier isoperated at a temperature just under a melting point of the ash, andunder a pressure not less than 6 bar gauge, and wherein the product gasstream comprises gaseous and particulate pollutants, the methodcomprising removing the pollutants from the product gas stream andproducing a waste water stream with a wet scrubber, and delivering atleast a portion of the waste water stream from the wet scrubber to a ashcooler connected with the gasifier which receives hot ash from thegasifier, wherein the waste water stream is converted into steam.

In some embodiment of the method, the ash cooler comprises a hightemperature ash cooler connected directly with the gasifier.

In some embodiment of the method, the ash cooler further comprises a lowtemperature ash cooler, and wherein at least a portion of the wastewater is delivered to the low temperature ash cooler.

In some embodiment of the method, the waste water makes direct contactwith the ash and steam generated from the contact is delivered to thegasifier.

BRIEF DESCRIPTION OF THE DRAWING

For the present disclosure to be easily understood and readilypracticed, the present disclosure will now be described, for purposes ofillustration and not limitation, in conjunction with the followingfigures.

FIG. 1 schematically shows an exemplary overall arrangement of thesyngas production system of the present invention, which comprises agasifier 1, a high temperature ash cooler 6, and a low temperature ashcooler 7. One or more cyclones 2 are provided for recovery and recycleof entrained solids from the crude syngas, with or without heat recoveryin a syngas cooler 3 in which boiler feed water is introduced and out ofwhich process steam is produced, with or without filters 4 to furtherclean the syngas. A wet scrubber 5 downstream of the gasifier isprovided to clean the syngas. Wastewater from the scrubber 5 can be fedto a high temperature ash cooler 6 or a low temperature ash cooler 7, orboth. When using direct contact cooling, upon contact with the hot ash,either in the high temperature ash cooler 6 or in the low temperatureash cooler 7, steam is generated. This steam can be fed back into thegasifier 1 (e.g. shown in the high temperature ash cooler 6), or befiltered in filter 8 and outputted for other purposes (e.g. shown in thelow temperature ash cooler 7).

FIG. 2 is a block diagram illustrating the sequential arrangement ofsteps to cool and depressurize the gasifier ash from gasifier conditionsto conditions suitable for safe and inexpensive ash handling, accordingto one embodiment of the present invention.

FIG. 3 illustrates the basic structure of a fluidized bed gasifieraccording to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A fluidized bed gasifier, as shown in FIG. 3, comprises a vessel housinga headspace 2 above a fluidized bed 1 of the solid material beinggasified and a conical perforated gas distribution grid 7 below the bedthrough which the gasifying medium is introduced at sufficient velocityto fluidize the solid feed material in the gasifier. The gasifyingmedium (steam and/or oxygen) is introduced into the gasifier from theplenum space 4 through the grid 7 to fluidize and partially oxidize thesolid feed stock.

A passage such as a pipe 6 (“center jet pipe”) in the center region atthe bottom of the grid cone introduces oxidant with diluting gas to thebed. Gas velocity of the centre jet pipe 6 is normally greater than theaverage superficial velocity of gas in the fluidized bed 1. An ashdischarge device 5 comprising an annular passage is provided around thiscenter jet pipe 6 for coal ash agglomerated withdrawal and also forprovision of additional gas, such as steam, which may serve to cool andprotect the center jet pipe 6. The ash discharge device 5 is oftenconfigured to comprise a venture 3 device for sorting the ash particlesat the upside of the passage. A classifier 8 can be intergraded with theash discharge device 5. A gas stream, such as steam, moving upwardsthrough the classifier, is often used to separate the ash particles,re-entraining those lighter and/or smaller particles whose carboncontent is not yet depleted and returning them back into the reactionregion,

As indicated above, handling of hot ash from the ash discharge device 5under high temperature as well as high pressure has been technicallychallenging in the coal gasification field. The present inventionprovides methods and related systems whereby the ash cooling process isseparated into respective steps and the first step is a first coolingstep under high pressure at high temperature. As shown in FIG. 1, thefirst cooling step under high pressure may be by indirect heat transferof ash with using indirect cooling medium or by direct contacting usingdirect evaporative cooling liquid. After the first cooling stepprocessed by the high temperature ash cooler (also referred as “highpressure ash cooler”), the temperature of the ash is low enough for theuse of conventional equipment. Therefore, further steps such as adepressurization step can be handled at low or medium temperature withequipments of lower cost, thus the investment of equipments is reducedand the reliability of all of the remaining ash handling equipment isalso increased.

In some embodiment, as shown in FIG. 2 , if a depressurization step isfurther performed, after depressurizing, the cooled and depressurizedash can then be cooled further in a low temperate ash cooler 7 andhandled using conventional methods. The stepwise system of the presentinvention recovers heat from said ash in such a manner as to raise theoverall efficiency of the gasification process.

A feature of the present inventive process is to first cool the ashexiting the gasifier in a high temperature cooler 6 at the gasifierpressure. The temperature of the ash after this high pressure ashcooling step may be determined based on two criteria. First thetemperature is high enough such that any steam generated from the hightemperature ash cooling has sufficient pressure and can be used toreplace part of the fluidizing and reacting steam needed for thegasifier. Second, the temperature of the ash is low enough to allow useof conventional carbon steel equipment, such as vessels, valves, pipes,and conveyors, for the subsequent ash handling. This lowers the cost andincreases the reliability of all of the remaining ash handlingequipments, particularly the equipment used to remove the ash from ahigh pressure environment to ambient pressure.

Although above two criteria are provided, it is understood so long as atleast one of two criteria are satisfied after this high pressure ashcooling step, the overall efficiency or reliability of the gasificationsystem can be improved. Also those skilled in the art can understandthat control the operating conditions in the ash coolers, such as theintroduction of cooling liquid or medium, by techniques in the priorart, e.g. valves, and other device for the adjustment etc., to controlthe ash temperature after the high pressure ash cooling step.

The gasification process requires a large amount of steam referred asprocess steam which is either be generated independently or by coolingthe syngas produced in the gasifier such as in a syngas cooler 3, asshown in FIG. 1, in the prior art, which is imposing a net energypenalty on the system. In comparison, in some embodiment of this presentinvention, the steam generated in the high temperature ash cooler can beused as port of the process steam, thereby allowing more steam to beexported from the gasification process, or reducing the need ofindependent steam generation. Thus, at least part of the energy penaltyon the gasifier system is released.

In some embodiment, referring FIG. 2, after the high temperature ashcooling, the lower-temperature ash is then depressurized using lowercost higher reliability equipment, such as carbon steel lock hoppers. Alow temperature ash cooling system follows, as shown as a lowtemperature ash cooler 7 in FIG. 2, which further cools the ash forordinary solids handling and disposal. The stepwise process of thepresent invention lowers capital cost, improves reliability, andimproves the overall efficiency of the gasification process.

In one aspect of the present invention, the system for gasifying acarbonaceous material comprises: 1) a gasifier into which thecarbonaceous material and gas feeds are fed and gasified to produce acrude syngas product leaving the gasifier from the top and also producehigh temperature ash under the operating pressure of the gasifierdischarged from the bottom of the gasifier, 2) an ash cooler, as suchthe high temperature ash cooler, connected with the gasifier, whereinthe ash cooler comprises i) a vessel to contain the ash during coolingand ii) an apparatus to cool the ash either via indirect heat transferor direct contact cooling, and iii) a connection to deliver thesteam(“vapor”) generated in step ii) back into the gasifier.

In one embodiment, the step-wise process of the present invention forcooling the high temperature and high pressure ash discharged from thegasifier comprises a first step wherein the free-flowing ash from thegasifier at the operating temperature of the gasifier is discharged,e.g. by gravity in the case of a fluidized bed gasifier, into acompartment or vessel, in which the ash is cooled. The operatingtemperature of the gasifier is usually a temperature just below themelting point of the ash e.g. 1200° C. The high-temperature ash coolingcompartment itself may be configured as a fluid bed or as a moving bed.

In one embodiment the high temperature ash cooler may be a “directcontact” cooler wherein water or other direct evaporative cooling liquidis directly contacted with the hot ash and converted to steam, whichflows countercurrent to the ash discharge into the gasifier via achannel connecting the gasifier to the high temperature ash cooler. Inthis way, the heat energy contained in the ash is used to generate steamwhich is used directly in the gasification reactor.

Direct contact may be affected by many methods well-known to thoseskilled in the art. For example, water, preferably atomized, may beinjected into the hot ash so long as the flow-ability of the ash ismaintained. This may be done via a water supply apparatus whichcomprises means to disperse the water into the ash such as spraynozzles, atomizing spray nozzles, microporous pipes, which for examplemay be made from sintered metal powder or fibers, pipes or other flowchannels with drilled holes. This direct contact cooling step can beachieved in either a moving bed or fluid bed ash cooler.

Indirect cooling can be used in combination with or instead of directcontact cooling. Whether this is means of jacketing of the vessel,cooling coils, or cooling panels or any other common means of indirectheat transfer, a indirect cooling medium is heated or evaporated in aflow channel separated from the ash. Steam is generated in the flowchannel and is relatively clean compared to the steam generated viadirect contact. Preferably, the steam is at a pressure higher than thatof the gasifier and can be used in the gasifier or for other uses.

After the high temperature cooler, the ash reaches a temperature atwhich any further handling or processing can be accomplished using e.g.ordinary carbon steel materials, which function well and reliably at atemperature below 500° C., preferably below 350° C. In one embodiment,after the high temperature ash cooler, the ash may be reduced inpressure, e.g. in a depressurizer, to ambient pressure for any furtherhandling or cooling. This can be achieved by a variety of means, such asvia valves and lock-hoppers well-known to those skilled in the art.These are conventional equipment and can operate rather reliably at atemperature of 300-550° C. even under the operating pressure of thegasifier.

A lock hopper is a well-known depressurizing device, and generallycomprises a vessel into and out of which the ash flows by gravity, withvalves at the top and bottom that seal against pressure and solids flow,and means to pressurize and depressurize the vessel, and associatedvalves and controls to regulate the gas flow.

The cooled and depressurized ash may optionally undergo a furthercooling step using a second cooler, or a low temperature ash cooler, forease of handling or safe disposal, e.g. to not more than 140° C. forhandling via belt conveyors. Any commonly available low pressure solidscooler, including a direct contact or indirect heat transfer cooler,e.g. a screw cooler, can be used as the low temperature ash cooler.

In the low temperature ash cooling step after depressurization, ascrubber blowdown (described below in detail) may be used in directcontact with the ash to provide cooling, transfer salts and suspendedsolids to the ash, and further recover water without salt for reuse,thus lowering wastewater treatment and reducing overall waterconsumption.

In some embodiment, a two-step cooling process (i.e. a high pressurecooling followed by depressurizing) of the present invention thus allowsthe overall cost of an ash cooling and depressurization system to belowered, its reliability increased, and the bulk of the heat availablein the ash, which is the heat of the ash from gasifier operatingtemperature to the exit temperature of the high temperature ash cooler,is directly converted to process steam. As mentioned above, the processsteam converted has the highest value possible for a gasifier system,for use in the gasifier without any addition steam handling.

In one embodiment, the high temperature cooler may also be designed tocool the ash to a lower temperature such that a low temperature ashcooler is not needed. Such a process may be desired if high processefficiency is needed, especially when the gasifier feed has high ashcontent. Such a lower temperature may be achievable even with directcontact cooling, so long as the water saturation pressure at the exittemperature of the high temperature ash cooler is above the gasifieroperating pressure.

In one embodiment, the high temperature cooler may also be designed tocool the ash to a lower temperature and the cooled ash is cooled by alow temperature ash cooler. In this embodiment, the depressurizer is notneeded. Such a process may be desired when the pressure of the cooledash is needed.

The above mentioned and other features of this invention and the mannerof obtaining and using them will become more apparent, and will be bestunderstood, by reference to the following drawing and description.

Referring to FIG. 1, hot ash passes from the gasifier 1 into the ashcooling apparatus. Depending on the operating conditions of the gasifier1, the hot ash may be at a temperature from 500° to 1200° C. at thedischarge point from the gasifier 1. The temperature of the ash leavingthe ash cooling device is determined by the operating pressure of thegasifier. As long as the saturation pressure of water at the ash exittemperature is above the gasifier operating pressure, water can beinjected directly into the moving or fluid ash.

The “pre-determined threshold temperature” may be determined by thefollowing two factors. Firstly, in order to keep the flowability of theash, liquid water should be avoided in the ash cooler. Thus, thetemperature of the cooled ash (T₁) should be kept at least above theboiling point of water at the ash cooling pressure. Preferably, thetemperature is at or above the critical temperature of water (i.e. 374°C.). Secondly, since the steam generated flows into the gasifier (moredetail below), the pressure of the steam should be above the pressure ofthe points at which the steam is introduced into the gasifier. Thus, thetemperature of the cooled ash (T₂) should be high enough. Therefore, thepre-determined threshold temperature should not be lower than either T₁or T₂.

In a preferred embodiment of the invention, the rate and amount of wateris controlled so that it is dispersed and mixes with the hot solidsproperly, and completely evaporates without affecting the flowability ofthe ash. The steam thus generated moves up into the reacting zone ofgasifier.

The flow of the cooling water can controlled by a flow control devicesuch as a control valve where the flow of the water is controlled bytemperature or pressure measurement in the ash cooler to regulate to theamount of cooling desired.

In this manner, the thermal energy contained in the hot ash is used togenerate steam needed for the gasification reaction, thus displacing theamount of clean, high pressure steam otherwise needed in thegasification reaction and typically generated in a separate boiler. Itshould be noted that the steam generated by direct contact with the ashis a “dirty” steam containing a variety of contaminants, making itunsuitable for most other purposes, but suitable for use in thegasification process.

The steam generated by direct or indirect contact can be introduced inthe gasifier through various points of the gasifier. As shown in FIG. 3,the steam can flow into the plenum space 4 via a channel and then beintroduced in the gasifier through the grid 7, or be introduced into thecenter jet pipe 6 as part of the jet gas, or through the classifier 8integrated with the ash discharge device 5. Since steam generated bydirect contact contains ash which may cause grid plug problem for thegrid 7, this direct contacting steam, preferably, is introduced to theclassifier 8, such as through the classifier gas inlet on the classifier8.

For example, in a SES gasifier (U.S. Ser. No. 13/532,769), if a 10 wt %ash feed stock is used, and the exit ash temperature is 1000° C., and iscooled to 400° C. Almost 1 kg of steam can be generated using thepresent invention for each 7 kg of ash which accounts for an appreciablefraction of the total gasification steam required.

Referring to FIG. 2, which illustrates the sequential arrangement ofsteps of one embodiment of the present process, the ash is first cooledto reach a temperature typically in the region of 300 to 550° C. in avessel of the high temperature ash cooler 6 at a pressure close to thegasifier pressure. The ash is then depressurized to ambient pressure viaequipment such as lock-hoppers. Regardless of the depressurizing methodused, for safety and maintenance purposes, some form of isolation valvemay be required between the high pressure region and the low pressureregion and this valve is far less expensive and more reliable at theexit temperature of the high temperature ash cooler than a valvespecified for service at temperatures (800 to 900° C.) near the gasifiertemperature (typically 1000° C. for the SES gasifier). Once the ash isat atmospheric pressure, it can be further cooled in a low temperatureash cooler 7 to safe handling temperatures, typically 50 to 140° C., inany number of manners using readily available solids cooling equipment.

Accordingly another aspect of the present invention, in anotherembodiment, the invention further provides a method and system of coalgasification wherein at least a part of wastewater stream generated fromone or more of the gas cleaning steps (e.g. the scrubber blowdown water)is recycled and applied to the hot ash residue from the gasificationprocess, in such a manner that the salts and suspended solids in thewaste water remain with the ash, wherein steam is generated in theprocess, which steam may be used for several purposes such as being fedback to the gasification process. The amount of water sent to wastewatertreatment of the system is reduced.

In one embodiment, the invention provides a system for gasifying acarbonaceous material, referring to FIG. 1, wherein the systemcomprises:

1) a gasifier 1 into which the carbonaceous material such as coal is fedand gasified to produce a crude syngas containing gaseous andparticulate pollutants;

2) optionally, at least one device to remove a portion of theparticulate pollutants and recycle the solids in the crude syngas suchas cyclone 2, cool the crude syngas such as syngas cooler 3;

3) optionally, another device to further remove solids from the gasstream, such as filter 4 as shown in FIG. 1;

4) a scrubber 5, wherein the cooled and partially cleaned syngas isfurther cleaned to produce a waste water stream;

5) at least one ash cooler connected with the gasifier to receive hotash under pressure from the gasifier, such as the high temperature ashcooler 6;

6) a connection to deliver at least a portion of the waste water streamto the ash cooler, wherein all or part of the waste water stream isconverted into steam; and

7) a connection to deliver the steam generated in the ash cooler backinto the gasifier.

According to an embodiment of the present invention, the waste waterstream from the scrubber can be delivered to either or both of the hightemperature ash cooler or low temperature ash cooler. Because the ashtemperature is much higher than the boiling point of water in either ofthe ash coolers, the water in the waste water stream, along with othervolatile components will evaporate, to generate a supply of steam, whileleaving the particulate pollutants and other non-volatile componentsbehind with the ash particles. The supply of steam from the hightemperature ash cooler is directed to the gasifier and supplements thesteam supply needed for the gasification process. Steam generated fromthe wastewater used in the low temperature ash cooler may be condensedin use as a low temperature heat source or the condensate used asprocess water makeup.

In one embodiment, this invention deals with the recycle of waste wateremanating from a water scrubber used for removing solids from productsyngas from e.g. a fluidized bed coal gasification process. Typically, awater scrubber follows the cyclones and filters (e.g. bag house filtersor candle filters) used to remove solids from the gas. This scrubbercaptures most, or nearly all, of the halide, ammonia, cyanides,remaining particulate matter not removed in the cyclones and filters,and some trace gas species that are at least partially water soluble.

Scrubbers, or wet scrubbers suitable for the present invention, arecommon and well-known devices that use liquid to wash and removeunwanted particulate and/or gas pollutants from a gas stream. There area diverse group of such devices that can be used. Scrubbers are one ofthe primary devices that control gaseous emissions, especially acidgases. Scrubbers can also be used for heat recovery from hot gases byflue-gas condensation. Wet scrubbing works via the contact of targetcompounds or particulate matter with the scrubbing solution, which maysimply be water. Water soluble toxic and/or corrosive gases like HCl,H₂S, SO₂ or ammonia (NH₃) can be removed very well by a wet scrubber.The water spray may also condense certain condensables such as tar andoil. Removal efficiency of pollutants is improved by increasingresidence time in the scrubber or by the increase of surface area of thescrubber solution by e.g. spraying.

According to one embodiment of the present invention, a portion (whichincludes all or none) of the waste water stream from the scrubber whichcontains the removed contaminants may be applied directly to contactwith hot gasifier ash at the gasifier operating pressure which istypically, but not restricted to, 10 to 60 bar. Alternatively, the wastewater stream may be applied in indirect heat transfer against the hotash, and substantially evaporated. In either case, the steam generatedfrom the cooling or the hot ash and any contaminants in the wastewaterstream that evaporate with the steam, can be re-introduced into thegasifier as part of the required steam for gasification purposes,reducing the overall water requirements for the gasification plant.

In another embodiment, a portion or all of the wastewater stream can beapplied to the ash directly in a low pressure ash cooling step. In thiscase, some of the water may be used to partially hydrate the ash fordust control in handling, for example raising the hot ash water contentfrom essentially zero to 5 wt %. Some of the water evaporates and thissteam may also be as a low temperature heat source with the condensatereused as process water, be vented, be sent to a flare, or condensed andreused as process water after removal of any entrained ash.

In another embodiment, the method of the present invention places thesalts and suspended solids from the wastewater into the ash product fromthe gasifier, reduces plant water consumption, and wholly or in parteliminates wastewater treatment for the gasification process. The highpressure steam generated from the direct injection of waste water to thehot ash can be directly connected to the gasifier, without having beencleaned to remove any entrained ash particles, thereby reducing the needfor high pressure clean steam, and resulting in significant increase inheat energy efficiency, yet only minimal increase in capital costs.

It is understood that examples and embodiments described herein are forillustrative purpose only and that various modifications or changes inlight thereof will be suggested to persons skilled in the art and are tobe included within the spirit and purview of this application and scopeof the appended claims. All publications, patents and patentapplications cited in this patent are hereby incorporated by referencefor all purposes.

One or more features from any embodiment maybe combined with one or morefeatures of any other embodiment without departing from the scope of thedisclosure. The above description is illustrative and is notrestrictive. Many variations of the invention will become apparent tothose skilled in the art upon review of the disclosure. The scope of theinvention should, therefore, be determined not with reference to theabove description, but instead should be determined with reference tothe claims along with their full scope or equivalents.

What is claimed is:
 1. A gasification system comprising: a fluidized bedgasifier into which a carbonaceous feed material is fed, and out ofwhich a product gas stream and a flowable ash is discharged, wherein thegasifier is operated at a temperature just under a melting point of theash, and under a pressure not less than 6 bar gauge, and a hightemperature ash cooler connected to the gasifier and into which the hotash under pressure is discharged, wherein the high temperature ashcooler comprises a water-supplying apparatus that provides water forcooling the flowable ash, wherein the flowable ash is cooled to atemperature suitable for the ash to be handled with conventional carbonsteel equipment.
 2. The gasification system of claim 1, wherein thewater supplying apparatus supplies the cooling water to the hightemperature ash cooler to be in direct contact with the flowable ash,and wherein the system further comprises a controller to control thewater supplying apparatus wherein the water is vaporized upon directcontact with the ash to generate steam, the flowability of the ash ismaintained, and the flowable ash is cooled to a temperature not lowerthan the pre-determined threshold temperature.
 3. The gasificationsystem of claim 1, wherein the cooling water is supplied to the hightemperature ash cooler and cools the ash via indirect heat transfer. 4.The gasification system of claim 3, wherein the high temperature ashcooler comprises a cooling jacket, or cooling coils, or a cooling panelthrough which the cooling water flows and absorbs heat indirectly fromthe hot ash.
 5. The gasification system of claim 1, wherein a portion ofthe cooling water is supplied to the high temperature ash cooler indirect contact with the flowable ash, and wherein the system furthercomprises a controller to control the water supplying apparatus so thatthe water is vaporized upon direct contact with the ash to generatesteam, and the flowability of the ash is maintained; and a portion ofthe cooling water is supplied to the high temperature ash cooler wherethe cooling water cools the ash via indirect heat transfer; and whereinthe flowable ash is cooled to a temperature not lower than thepre-determined threshold temperature.
 6. The gasification system ofclaim 1, further comprising a connection between the high temperatureash cooler and the gasifier, wherein steam generated from the watersupplied to the high temperature ash cooler is supplied to the gasifier.7. The gasification system of claim 1, further comprising: adepressurizing device which is connected to the high temperature ashcooler to receive the cooled high pressure ash from the high temperatureash cooler, and which is able to reduce the pressure of the ash toambient pressure.
 8. The gasification system of claim 7, wherein thedepressurizing device comprises a double sealed lock hopper.
 9. Thegasification system of claim 1, further comprising: a second ash coolerdevice which is connected to the high temperature ash cooler to receivethe cooled high pressure ash from the high temperature ash cooler, andwhich is able to further lower the temperature of the ash to ambienttemperature.
 10. The gasification system of claim 7, further comprising:a second ash cooler device which is connected to the depressurizingdevice to receive the ash from the high temperature ash cooler, andwhich is able to further lower the temperature of the ash to ambienttemperature.
 11. The gasification system of claim 9, further comprising:a depressurizing device which is connected to the second ash coolingdevice to receive the ash from the second ash cooling device, and whichis able to reduce the pressure of the ash to ambient pressure.
 12. Thegasification system of claim 2, wherein the high temperature ash coolercomprises a fluidized bed or a moving bed wherein the high pressure ashmakes direct contact with the water from the water supplying apparatus.13. The gasification system of claim 2, wherein the water supplyapparatus comprises means to disperse the liquid into the ash such asspray nozzles, atomizing spray nozzles, microporous pipes.
 14. Agasification system comprising: a fluidized bed gasifier into which acarbonaceous feed material is fed, and out of which a product gas streamand a flowable ash are discharged, wherein the gasifier is operated at atemperature just under a melting point of the ash, and under a pressurenot less than 6 bar gauge, and wherein the product gas stream comprisesgaseous and particulate pollutants, a wet scrubber for removing thepollutants from the product gas stream and producing a waste waterstream, an ash cooler connected with the gasifier to receive hot ashfrom the gasifier; and a connection to deliver at least a portion of thewaste water stream to the ash cooler, wherein the waste water stream isconverted into steam.
 15. The gasification system of claim 14, whereinthe ash cooler comprises a high temperature ash cooler connecteddirectly with the gasifier.
 16. The gasification system of claim 15,wherein the ash cooler further comprises a low temperature ash cooler,and wherein at least a portion of the waste water is delivered to thelow temperature ash cooler.
 17. The gasification system according toclaims 15, wherein the waste water makes direct contact with the ash andsteam generated from the contact is delivered to the gasifier.
 18. Amethod for cooling ash discharged from a fluidized bed gasifier, whereina fluidized bed gasifier is fed with a carbonaceous feed material, and aproduct gas stream and a flowable ash is discharged out of the gasifier,wherein the gasifier is operated at a temperature just under a meltingpoint of the ash, and under a pressure not less than 6 bar gauge, themethod comprising: cooling the flowable ash to a temperature suitablefor the ash to be handled with conventional carbon steel equipment in ahigh temperature ash cooler which is connected to the gasifier and intowhich the hot ash under pressure is discharged, wherein the hightemperature ash cooler comprises a water-supplying apparatus thatprovides water for cooling the flowable ash.
 19. The method according toclaim 18, wherein the water supplying apparatus supplies the coolingwater to the high temperature ash cooler to be in direct contact withthe flowable ash, and the method further comprises controlling the watersupplying apparatus so that the water is vaporized upon direct contactwith the ash to generate steam, and the flowability of the ash ismaintained, and the flowable ash is cooled to a temperature not lowerthan the pre-determined threshold temperature.
 20. The method accordingto claim 18, further comprising: receiving the cooled high pressure ashfrom the high temperature ash cooler, and reducing the pressure of theash to ambient pressure with a depressurizing device which is connectedto the high temperature ash cooler.
 21. The method according to claim20, further comprising: receiving the cooled ambient pressure ash fromthe a depressurizing device, and further lowering the temperature of theash to ambient temperature with a second ash cooler device which isconnected to the depressurizing device.
 22. A method for cooling ashdischarged from a fluidized bed gasifier, wherein a fluidized bedgasifier is fed with a carbonaceous feed material, and a product gasstream and a flowable ash are discharged out of the gasifier, whereinthe gasifier is operated at a temperature just under a melting point ofthe ash, and under a pressure not less than 6 bar gauge, and wherein theproduct gas stream comprises gaseous and particulate pollutants, themethod comprising: removing the pollutants from the product gas streamand producing a waste water stream with a wet scrubber, delivering atleast a portion of the waste water stream from the wet scrubber to a ashcooler connected with the gasifier which receives hot ash from thegasifier, wherein the waste water stream is converted into steam. 23.The method according to claim 22, wherein the ash cooler comprises ahigh temperature ash cooler connected directly with the gasifier. 24.The method according to claim 23, wherein the ash cooler furthercomprises a low temperature ash cooler, and wherein at least a portionof the waste water is delivered to the low temperature ash cooler. 25.The method according to claims 23, wherein the waste water makes directcontact with the ash and steam generated from the contact is deliveredto the gasifier.